塔里木盆地乌什凹陷白垩系冲积扇—扇三角洲沉积相及有利储盖组合

Alluvial Fan and Fan-delta Sedimentary Facies and Favorable Assemblage of Reservoir and Seal of Wushi Sag(Cretaceous) in Tarim Basin

通过对乌什凹陷南缘坳陷乌参1井及北缘露头剖面地详细观察,结合测井曲线形态和地震剖面综合分析,乌什凹陷北部和南部由于受构造条件、古气候和物源的影响,发育了截然不同的沉积相类型,北缘露头区以滨浅湖相沉积为主,南部坳陷区则发育了典型的冲积扇—扇三角洲粗粒沉积相。这套沉积碎屑岩颗粒粒度悬殊且不连续,砾岩和砂岩间常显示粒度不连续的现象,剖面中巨厚层砾岩常与中厚层细砂岩、粉砂岩、泥岩沉积层直接接触,无过渡性粒级存在。造成这种现象的主要原因是由于北缘露头区处于相对稳定的构造条件及较远的物源条件,而南缘坳陷区由于靠近温宿凸起物源并受断裂控制。乌什凹陷发育两套较好的储盖组合,分别是亚格列木组—舒善河组中下部砂砾岩与舒善河组泥岩、含膏泥岩和巴什基奇克组—库姆格列木群底砂砾岩与库姆格列木群盐层、含膏泥岩。乌参1井已在第一套储盖组合中的舒善河组中下部的扇三角洲砂体中获得重大发现,这些砂体为扇三角洲前缘的砂坝、辫状河水道充填可形成较好的储层。第二套储盖组合中巴西盖组和巴什基奇克组的砂体分布广泛,岩性较致密;储层厚度较大,纵向发育集中,但物性较差,总体上属于一套中等储盖组合,预测离物源区一定距离应分布有优质储集相带。

Based on Wucan 1 well of the south depression and the noah outcrop section in Wushi sag, and in combination with synthetic analysis with logging shape and seismic section, it can be seen that the study area develops much different sedimentary facies of the noah and south in the Wushi sag due to the structural influence, palaeoclimate and source. The noah outcrop section mainly develops shore shallow lake sedimentary facie, yet the south depression develops typical course grain alluvial fan and fan-delta sedimentary facies. The elastic rock grain of this sedimentary facies is great different and discontinuous. The extremely thick conglomerate usually contacts directly with fine sandstone, sihstone, mudstone without transition grain. The main reason come from condition of the noah outcrop locating on stable structure and having farer source, but the south depression owing to the close to source of Wensu swelling and being controlled by fractures. There are two sets of combination about reservoir and seal in Wu Shi sag as follows, one is conglomerate of middle-lower strata of Yageliemu Formation-Shushanhe Formation and mudstone and gypsum mudstone of the Ku Mu Ge Lie Mu Formation, the other is the bottom glutenite of the Bashenjiqike Formation-Kumugeliemu Formation and the salt bed and gypsum mudstone of the Kumugeliemu Formation. It has been acquired oil and gas form the first set of of combination about reservoir and seal of the middle-bottom fandelta sandstone of fan- delta front facie, which belong to the sand bar and braided channel and can from better reservoir. The sandstone of the second set of combination about reservoir and seal of the Baxigai Formation and Bashijiqike Formation has widespread distribution with dense lithology and the reservoir is very thick and longitudinal concentricity, poor porosity and permeability. Generally, it belongs to the medium reservoir and seal combination. Owing to the poor exploration, it is predicted that there is high quality reservoir facies formed in distal area from the source.